1,4,6-Trimethyl-9-trifluoroacetyl'uorene I has been synthesized in one potfrom 2chloro-p-qlene 2 and has been characterized by single-crystal X-ray diffraction. O 1997 Elsevier Science Ltd.
Lithium piperidide in ether has been reported to be a better benzyne-producing reagent than phenyllithium, whereas the generated benzyne, given a choice, reacts preferentially with phenyllithium over piperidide.1 However, a 1 : 1 mixture of the two reagents in tetrahydrofuran ('H-IF),when treated sequentially with 2-chloro-p xylenez (2) and then ethyl tri.fluoroacetate, afforded the substituted fluorene 1 in 8ZZ0 yield, rather than the expected 3,6-dimethyl-2-phenyl-a, ct,ct-trifluoroacetophenone3.3
This result can be rationalized by the series of reactions shown in Scheme 1. If competitive deprotonations take place at position 3 and at the benzylic position of 2, to yield 4 and 5, respectively, 4 can generate benzyne 6, which then reacts preferentially with 5, rather than with either phenyllithium or lithium piperidide. The other benzylic position of 2 is not deprotonated, since no 1,4,7-trirnethylfluot.ene isomer of 1 has been observed. This suggests that the formation of 5 is favored by complexation effects involving lithium and the ortho-chlorineatom,